convert some methods in designs and graphs to n_*

[fchapoton]

This replaces methods num_points and num_blocks by n_points and n_blocks in designs.

Old names are kept as aliases.

cf also #40875

This is just a small reduction of the number of method with names num_*

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[vincentmacri]

Thanks for the contribution!

If you want the aliases to be deprecated eventually you can use this: https://doc.sagemath.org/html/en/reference/misc/sage/misc/superseded.html#sage.misc.superseded.deprecated_function_alias

If you don't want the aliases to get deprecated then this is fine. My suggestion to change the functions that return int to Integer is an "if you want to" suggestion, this PR is already an improvement and I won't insist on expanding the scope.

I'm happy with this as-is, if you are too feel free to set to positive review. If you want to make the additional changes I suggested (marking the functions as deprecated aliases or changing int to Integer) then tag me when it's ready for review again.

[vincentmacri]

I just saw the discussion in #40875 about deprecations, I take back my suggestion to deprecate the aliases since there are some good reasons to not deprecate these names. If you want to make the int to Integer change feel free and I'll review it again, otherwise you can set this to positive review.

[fchapoton]

thanks for the review. I choose to set to positive.

[mantepse]

@fchapoton, will you also do the remaining num_xxx? If you don't, I would just introduce aliases for the following:

coding/binary_code.pyx:1893:    cdef int num_cells(self, int k) noexcept:
databases/knotinfo_db.py:239:    def num_knots(self, version):
graphs/base/c_graph.pyx:1421:    def num_edges(self, directed):
graphs/base/c_graph.pyx:1524:    def num_verts(self):
graphs/base/graph_backends.pyx:586:    def num_edges(self, directed):
graphs/base/graph_backends.pyx:608:    def num_verts(self):
graphs/base/static_sparse_backend.pyx:983:    def num_verts(self):
graphs/base/static_sparse_backend.pyx:1046:    def num_edges(self, directed):
graphs/generic_graph.py:6990:    def num_faces(self, embedding=None):
groups/perm_gps/partn_ref/refinement_python.pyx:117:    def num_cells(self):
knots/knotinfo.py:874:    def num_components(self):
lfunctions/pari.py:578:    def num_coeffs(self, T=1):
lfunctions/dokchitser.py:348:    def num_coeffs(self, T=1):
modular/modform_hecketriangle/hecke_triangle_group_element.py:2739:            sage: def num_linking_number(A, z, n=3, prec=10, num_prec=53):
modular/etaproducts.py:665:def num_cusps_of_width(N, d) -> Integer:
schemes/product_projective/space.py:566:    def num_components(self):